1. Field of the Invention
The present invention relates to a web fed printing machine including a misregistration eliminating apparatus for eliminating misregistration that arises in the process of superimposition printing performed by a preceding printing unit and a subsequent printing unit disposed separately from the preceding printing unit. More particularly, the invention relates to a web fed printing machine including a misregistration eliminating apparatus for eliminating misregistration that arises between an image printed by a preceding printing unit and an image printed by a subsequent printing unit disposed separately from the preceding printing unit after web rolls are spliced together through pasting in the process of superimposition printing performed by the printing units.
2. Description of the Related Art
Conventionally, a web fed printing machine includes a misregistration eliminating apparatus for eliminating misregistration that arises between an image printed by a preceding printing unit and an image printed by a subsequent printing unit, the printing units being disposed separately, after web rolls are spliced together through pasting in the process of superimposition printing performed by the printing units. Such a misregistration eliminating apparatus is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 57-170761.
The disclosed misregistration eliminating apparatus includes compensator roller means, which is disposed midway between two printing units and can increase or decrease the length of a web path. When a pasting end signal indicative of end of splicing of web rolls is generated, the compensator roller means operates in such a direction as to increase the web path length by a predetermined length. Subsequently, every time web is consumed by a predetermined length, the compensator roller means operates in such a direction as to decrease the web path length by a length obtained by dividing the increment (increase) in web path length by a certain integer. The compensator roller means continues the decremental action under automatic control until the increment in web path length is decreased to “0.”
The above-mentioned increment in web path length, a decrement in web path length at every action of decreasing the web path length, and the length of web to be consumed between actions of decreasing the web path length can be set as appropriate in consideration of the type and quality of a web roll to be used.
The above control prevents occurrence of misregistration. Specifically, in the case where printing is performed on a portion of a web that is drown out from an outer peripheral portion of a web roll and thus exhibits a large degree of elongation, the web path length is increased in order to prevent occurrence of misregistration which could otherwise result from the large degree of elongation. In the case where printing is performed on a portion of the web that is drown out from an intermediate or central portion of the web roll and thus exhibits a small degree of elongation, the web path length is decreased in an appropriate number of decremental actions in accordance with the length of web drawn out from the web roll until the increment in web path length is decreased to “0,” thereby preventing occurrence of misregistration which could otherwise result from gradual tendency of web run toward misregistration if printing was continued with the web path length left increased.
The disclosed misregistration eliminating apparatus performs the following control without confirmation of the condition of registration of printed images: after pasting, the length of the web path extending midway between a preceding printing unit and a subsequent printing unit is increased; subsequently, every time web is consumed by a constant length, the increment in the web path length is decreased by a length obtained by dividing the increment in the web path length by a certain integer. Furthermore, control items; specifically, an increment in web path length, a decrement in web path length at a single action of decreasing the web path length, and the length of web to be consumed between start of an action of decreasing the web path length and start of the subsequent action of decreasing the web path length are set as appropriate in consideration of the type and quality of a web roll to be used.
Thus, obtaining printed images with high accuracy of registration is almost impossible. Even when a target accuracy of registration is lowered slightly, parameters that must be considered when the above-mentioned control items are to be set are not limited to the type and quality of a web roll to be used, but further include temperature and humidity at the time of work. Therefore, a very high level of skill is required.